The present invention relates to a photocatalytic powdered water based paint, i.e. a powdered compound that becomes a water based paint once diluted in water, that has considerable advantageous characteristics in addition to its main property of converting pollutants present in the air by photocatalysis, it being also able to remove bad smells, to prevent mould and bacterial cultures from developing on the supports painted therewith, as well as to prevent dark marks from developing on the surfaces because of its self-cleaning function and to prevent heat from being transmitted by reflecting the sunbeams.
Moreover the water based paint of the present invention is highly eco-friendly as it does not contain harmful products such as heavy metals (cadmium, mercury, arsenic, lead, hexavalent chromium), its content of volatile aromatic hydrocarbons (benzene and derivatives, toluene, o-xylene, styrene) is practically negligible, its content of volatile organic compounds (VOC) is less than 0.5 g/l, therefore it lends itself excellently to the application on any surfaces both made of stones and of metal or plastic, both for interiors and exteriors, in order not to alter over time the original appearance of buildings, monuments, public works of any kind.
Photocatalytic compositions have been known and used for some time for preserving the original appearance of cementitious, stone or marble structures protecting them from being attacked by pollutants in the air, by atmospheric agents and by the several difficulties generated by the present environmental conditions developed by the modern society. Examples of photocatalytic compositions based on titanium dioxide mixed with various additives are known for example in documents EP0784034, EP0633964, EP1196359, EP1944279, WO 2008/017934, WO 2009/080647 and WO 2010/012488. Although such compositions have led to satisfactory results, there is still the need for further improvements in order to overcome drawbacks, even important ones, that have not been solved by such compositions.
Among such drawbacks it is of particular importance the fact that their application is possible only by spraying them or by using a roller, while by the use of the brush the product does not spread leaving the so called brush marks, that is brush strokes are in relief resulting in a not much satisfactory aesthetical appearance; moreover the maturing of the product and its mechanical strengths over time resulted in a chalking of the paint; other drawbacks were the difficulty in application, hiding power, non optimal point of white and mechanical performances; and the possibility of the formation of efflorescences due to the phenomenon of hydrolysis lime.
Further examples of photocatalytic compositions based on titanium dioxide mixed with various additives are disclosed in documents WO 2009/013337 and U.S. Pat. No. 6,406,536 that, however, are not able to give an optimal photocatalytic activity to the paint.
All these problems have been solved with a long lasting work studying problems, trials, tests and analyses, that have led to the selection of optimal ingredients and have led to the realization of the excellent photocatalytic water based paint of the present invention.
In particular, it has been surprisingly found that excellent photocatalytic characteristics are given to paint by using nanoparticle material.
In order to achieve a real and effective improvement of the water based paint, several searches and tests have been accomplished on the several types of raw materials, starting from a standard laboratory mixture composed of photocatalytic cement as a binder and as fundamental matrix for photocatalysis development, micronized limestone and of very low viscosity cellulose, to which additives have been added from time to time in order to solve each problem initially related to such type of water based paint. Tests represented below show the real efficacy of the new additives in comparison to other additives of the same type that were used previously. The overall final mixture constituting the water based paint according to the present invention derives from all the new additives investigated in said tests that are incorporated therein and therefore, the composition of said final mixture, used later for performing the production tests, is shown below in this document, after discussing said tests.
More precisely, said photocatalytic cement, used as a binder and as fundamental matrix for photocatalysis development, is Portland cement admixed with nanoparticle photocatalytic Titanium Dioxide, the size of said Titanium Dioxide nanoparticles being lower than 5 nanometers (thousandths of micron); even more precisely, said photocatalytic cement is white Portland cement, this colour, substantially given by the Titanium Dioxide, being preferable in order to be able subsequently, in case, to colour the cement (which is hardly feasible from grey colour).
As previously stated, it has been surprisingly found that excellent photocatalytic characteristics are given to paint by using nanoparticle material; it is believed, without intending to be bound by this theory, that the nanoparticle material activates the photocatalysis making effective the release of an electron, specifically when a product painted with the paint according to the present invention is hit by a light with a wavelength of about 380 μm.
More precisely, said micronized limestone is inert limestone with a maximum grain-size distribution lower than 100 microns.
More precisely, said very low viscosity cellulose is cellulose with viscosity lower than 1,000 mPas; it is here considered useful to specify that the average viscosity of a cellulose is about 13,000-15,000 mPas, it is high over 20,000 mPas and it is very low below 1,000 mPas.
More precisely, the additives intended for solving specific problems are a fluidizer, an antifoam, a vinyl polymer and pigments; even more precisely, at least one and preferably all the following additional additives are comprised: metakaolin, calcium formate and kieselguhr.
Preferably, said fluidizer is a polycarboxylic acid fluidizer and said vinyl polymer is a hydrophobized vinyl polymer.
For clarity's sake we want here to point out that, in the present description, the technical term “hydrophobized” means the water repellence property, i.e. the ability to repel water, that is intended to be given to a product.
Preferably, said pigments are coated with a cellulose-based film that, when comes in contact with water, dissolves releasing the pigment, said film preferably dissolving in a time lower than 2 seconds and more preferably in less than 1 second; moreover, preferably, said pigments are formed into granules whose dimensions have a grain-size range from 200 to 500 microns.
Preferably the composition according to the present invention further comprises low photocatalytic activity Titanium Dioxide, which serves to increase the paint whiteness.